The present invention relates in general to electrified vehicles using a high voltage bus, and, more specifically, to detecting isolation faults (i.e., leakage) occurring at a load side of an inverter drive.
Electrified vehicles such as for electric vehicles and hybrid electric vehicles typically utilize a high voltage power bus driven by a DC power source which may include storage and/or conversion devices such as a multi-cell battery pack or a fuel cell. The presence of high-voltage buses creates a need for monitoring of the electrical isolation of each bus with respect to the electrically conductive components of the vehicle chassis (ground).
The leakage resistance present between a DC bus and chassis ground must be sufficiently large to maintain safety and to comply with regulations. A typical leakage detector circuit operates by periodically connecting one bus at a time to chassis ground through a current-limiting resistance, and using the resulting current flow (e.g., voltage drop across the resistance) to calculate the leakage resistance between the opposite bus and ground. The battery voltage divided by the calculated leakage resistance characterizes the electrical isolation. An example of DC bus leakage detection is provided in U.S. application Ser. No. 14/104,243, entitled “Leakage Detection Circuit with Integral Circuit Robustness Check” filed Dec. 12, 2013, incorporated herein by reference in its entirety.
A typical component in an electric drive system is a Battery Energy Controller Module (BECM) that includes or can be programmed to include various battery management and communication functions as well as monitoring battery cell voltage production, current flow, temperature, and other parameters. Detection of DC bus leakage resistance may typically be implemented using the BECM for controlling the detector switches and measuring the detector voltages. Various battery monitoring integrated circuit devices have been developed commercially for use in the vehicle environment. Examples of a commercially available battery monitoring IC device include the AD7280A device available from Analog Devices, Inc., of Norwood, Mass., the LTC6804 device available from Linear Technology Corporation of Milpitas, Calif., and the ISL94212 Multi-Cell Li-Ion Battery Manager available from Intersil Corporation of Milpitas, Calif.
DC bus leakage detection as described above is responsive to isolation faults occurring on the DC input side of an inverter that couples the DC buses to an AC traction motor and/or generator. It is likewise necessary to detect isolation faults on the AC side of the circuit including the AC traction motor or generator and the wiring cables from the inverter to the motor/generator. However, the detection of isolation faults in the AC circuit have required separate detectors or other monitors connected to the AC circuits, resulting in added cost and complexity.